Silica and carbon black have been commonly used as reinforcing agents and/or fillers in rubber and thermoplastic polymers. A number of techniques have been developed to incorporate such reinforcing agents and fillers into the polymer compositions, including both wet and dry blending processes. The incorporation of such silica and carbon black as reinforcing agents and/or fillers is far more complex than might otherwise appear. One problem in wet blending of silica with lattices of such polymers arises from the fact that the hydrophilic silica has a tendency to associate with the aqueous phase and not blend uniformly with the hydrophobic polymer and the fillers.
Perhaps the most commonly employed practice, used commercially, is the technique of dry blending either silica, carbon black or both of them into rubber and thermoplastic polymers in a high-shear milling operation. That practice has many limitations. Notable among them include the tendency of the filler particles to agglomerate to each other, resulting in non-uniform dispersion of the filler throughout the polymer constituting the continuous phase.
Another problem commonly experienced in such high-shear milling operations is the tendency of the polymers to degrade during milling. Milling necessitates the use of higher molecular weight polymers, which sometimes require the incorporation of various types of processing aids to facilitate mixing and dispersion of the filler particles into the polymer constituting the continuous phase. The cost associated with the use of such processing aids also increases the manufacturing cost of the polymeric compound or article. The use of processing aids has the further disadvantage in that such processing aids may have a negative effect on the cure or end use of the polymer. And, in addition, dry blending techniques add additional processing costs, in part due to the accompanied excessive equipment wear by the abrasive fillers.
There is a need to provide a simple and less expensive technique for the uniform incorporation of silica with other fillers into natural and synthetic polymer latexes which do not require the use of complex processing aids.
There is also need to provide a process for the incorporation of silica which reduces sulfur content in the resultant rubber, into natural and synthetic polymers at the latex stage which is simple and inexpensive.
Another need is to provide a process for the incorporation of silica reinforcing agent into natural and synthetic polymers in which the silica can be substantially uniformly dispersed and the nanomaterial can be uniformly dispersed while forming a stable polymer matrix during processing for end use. Nanomaterial is small particulate material with each particulate having a diameter ranging only from 10 to 50 microns.
A need exists for a silica, compatible with natural and synthetic polymers, having two different organic coatings chemically bonded on the silica surface.
The present embodiments meet these needs.